This invention relates to a method for producing a cellulose acylate film by a solution-casting method.
Cellulose acylate film is usually produced by a solution-casting method. By the solution-casting method, a solution of cellulose acylate, hereinafter referred to as a dope, is poured onto an endless metal support having a mirror plane through a die arranged upward the support so as to evaporate the solvent of the dope from the poured layer of the dope. The layer of the dope from which the solvent is evaporated is referred to as a web. The web, is peeled off from the metal support by a peeling roller when the remaining amount of the solvent is attained at a prescribed amount. Then the web is dried while the web is transported by a roller or a tenter to produce the cellulose acylate film.
In the solution-casting film producing method, the production was usually performed at a transportation speed of not more than 40 m/min. Recently, however, the demand for the cellulose acylate film is considerably increased. Accordingly, raising in the production speed or the transportation speed is strongly required to raise the supplying amount of the film.
However, it has been found that serious problems are raised on the surface structure and the flatness of the film. In the usual production performed with the transportation speed of not more than 40 m/min., the web has been peeled off in a state having a remaining solvent content of not more than 40%. It has been found by the inventors that the peeling ability of the web is considerably degraded when the remaining solvent content exceeds 40%, but improved again when the solvent content is increased over a certain value. It has been also found that the problem of peeling ability has related to not only the remaining solvent content but also some factors such as the difference between the temperature at the peeling time and that after the peeling and the surface properties of the roller to be firstly contacted to the web just after the peeling. This invention is attained based on such the knowledge.
The object of the invention is to provide a method for producing a cellulose acylate film by which the cellulose acylate film excellent in the flatness and the surface quality with a little curing, wrinkle, unevenness, and defect caused by pressure, can be produced even when the transportation speed is accelerated. The web can be easily peeled off from the metal support and the peeled web can be stably transported and dried by the method according to the invention.
The invention and embodiments are described below.
A method for producing a cellulose acylate film comprising the steps of
casting dope containing cellulose acylate and solvent on a surface of a metal support,
peeling off a web formed by casting the dope from the metal support, and
drying the peeled web,
wherein remaining content of the solvent in the web when the web is peeled off is within the range of from 70 to 120%,
contacting surface of the web with a first roller just after the peeling off of the web from the metal support surface, consequently,
surface temperature of the first roller Tr is controlled so that the relation of the Tr and the surface temperature of the metal support at the time of peeling Tb is (Trxe2x88x92Tb)xe2x89xa650xc2x0 C., and
surface roughness Rmax of the first roller is not more than 1.0 xcexcm.
A method for producing a cellulose acylate film mentioned above wherein the web is contacted to the first roller within 5 seconds after peeled from the metal support.
A method for producing a cellulose acylate film mentioned above wherein transportation speed of the web is preferably within the range of from 40 m/min. to 120 m/min.
A method for producing a cellulose acylate film mentioned above wherein surface temperature of the first roller is gradually decreased from central portion to both end of the roller along longitudinal direction of the roller.
A method for producing a cellulose acylate film mentioned above wherein the web comes into contact with the first roller on the surface of the web which has been exposed to air on the metal support.
A method for producing a cellulose acylate film mentioned above wherein the web comes into contact with the first roller on the surface of the web which has been contacted with the metal support, and consequently a second roller on the surface of the web which has been exposed to air on the metal support.
A method for producing a cellulose acylate film mentioned above wherein diameter of the first roller is gradually decreased from both end to the central portion of the roller along the longitudinal direction of the roller.
A method for producing a cellulose acylate film mentioned above wherein diameter of the first roller is gradually increased from both end to the central portion of the roller along the longitudinal direction of the roller.
A method for producing a cellulose acylate film mentioned above wherein the first roller is a nipping roller.
A method for producing a cellulose acylate film mentioned above wherein each both edges of the web after peeling off from metal support comes contact with two rollers, so that the angles of the axis of each of the roller with the direction perpendicular to the transportation direction of the web are xcex8 and (180xc2x0xe2x88x92xcex8xe2x80x2), respectively, and xcex8 and xcex8xe2x80x2 are each satisfy the condition of
xe2x80x83xcex8 greater than 0xc2x0 and xcex8 less than 90xc2x0.
A method for producing a cellulose acylate film mentioned above wherein position of the first roller is varied so that the angle formed by the web with the metal support keeps constant at a point where the web is peeled off from the metal support.
A method for producing a cellulose acylate film mentioned above wherein position of the first roller is varied according to remaining solvent content or surface temperature of the web at the time of peeling of the web from the metal support.
A method for producing a cellulose acylate film mentioned above wherein air is blown with a flow rate of not less than 20 m/second to the surface of the web at side which has been contacted to the metal support after peeling off from the metal support.
A method for producing a cellulose acylate film mentioned above wherein the web comes into contact with the first roller and then a second roller, wrapping angle of the web with the first roller being varied by changing position of the second roller corresponding to content of remaining solvent or surface temperature of the web at a position where the web is peeled off from the metal support. In one of the embodiment, the diameter of the first roller is preferably decreased from both ends to the center of the roller.
In the other embodiment, the diameter of the second roller is preferably increased from both ends to the center of the roller.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web form a metal support,
firstly passing the web between a pair of nipping rollers, and
drying the web.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web from a metal support,
touching two small rollers to each the both edges of the surface of the web, which has been contacted to the metal support, just after the peeling off of the web from the metal support surface, so that the angles of the axis of each of the roller with the surface of the web are xcex8 and (180xc2x0xe2x88x92xcex8xe2x80x2), respectively, and xcex8 and xcex8xe2x80x2 are each satisfy the condition of
xcex8 greater than 0xc2x0 and xcex8xe2x80x2 less than 90xc2x0, 
thereafter, contacting the surface of the web which has been exposed to air on the metal support, to the first roller, and
drying the web.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web from a metal support,
contacting the web to a first roller, the position of which is varied corresponding to the content of remaining solvent in the web at a time just after the web is peeled or the surface temperature of the web at the time of peeling, and
drying the web.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web from a metal support,
vertically blowing air at a speed of not less than 20 m/second onto the surface of the web, which has been contacted with the metal support, through a slit arranged at a position upward the web,
contacting the face of the web which has been exposed to air on the metal support, to the first roller, and drying the web.
(8) The distribution in the across direction of the web of the flow rate of air vertically blown to the web through the slit is preferably gradually increased from the center to the both ends of the web.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web from a metal support,
contacting the web to a first roller,
then contacting the web to a second roller, and
drying the web,
wherein the wrapping angle of the web to the first roller is varied corresponding to the content of solvent remaining in the web at the time of peeling by varying the position of the second roller.
The surface temperature of the surface of the first roller preferably has a distribution in which the temperature is gradually decreased from the central portion in the longitudinal direction of the roller to the both ends of the roller.
A method for producing a cellulose acylate film by a solution-casting method comprising the steps of
peeling off a web from a metal support,
contacting the web to a first roller, and
drying the web,
wherein the surface temperature of the first roller Tr is controlled so that the relation of the Tr and the surface temperature of the metal support at the time of peeling Tb is (Trxe2x88x92Tb)xe2x89xa650xc2x0 C.
The surface temperature Tr of the roller preferably has a distribution in which the temperature is gradually decreased from the central portion in the longitude direction of the roller to the both ends of the roller.
In the method for producing a cellulose acylate film the surface roughness Rmax of the roller to which the web is firstly contacted in preferably Rmaxxe2x89xa61.0 xcexcm.